LITERATURE REVIEW

QUANTIFYING THE HIGH-VELOCITY, LOW-AMPLITUDE

SPINAL MANIPULATIVE THRUST: A SYSTEMATIC REVIEW

Aron S. Downie, MChiro,a Subramanyam Vemulpad, MSc, PhD,b and Peter W. Bull, DC, MAppScc

a Contract TecMacquarie Unive

b Director of Utic, Macquarie U

c Senior LectuPostgraduate StuUniversity NSW

Submit requeEvan St, Wollong(e-mail: aron.dow

Paper submitt2010; accepted J

0161-4754/$3Copyright ©doi:10.1016/j.

542

ABSTRACT

Objectives: The purpose of this studywas to systematically review studies that quantify the high-velocity, low-amplitude(HVLA) spinal thrust, to qualitatively compare the apparatus used and the force-time profiles generated, and to criticallyappraise studies involving the quantification of thrust as an augmented feedback tool in psychomotor learning.Methods: A search of the literature was conducted to identify the sources that reported quantification of the HVLAspinal thrust. MEDLINE-OVID (1966-present), MANTIS-OVID (1950-present), and CINAHL-EBSCO host (1981-present) were searched. Eligibility criteria included that thrust subjects were human, animal, or manikin and that thethrust type was a hand-delivered HVLA spinal thrust. Data recorded were single force, force-time, or displacement-time histories. Publications were in English language and after 1980. The relatively small number of studies,combined with the diversity of method and data interpretation, did not enable meta-analysis.Results: Twenty-seven studies met eligibility criteria: 17 studies measured thrust as a primary outcome (13 human, 2cadaver, and 2 porcine). Ten studies demonstrated changes in psychomotor learning related to quantified thrust data onhuman, manikin, or other device.Conclusions: Quantifiable parameters of the HVLA spinal thrust exist and have been described. There remain anumber of variables in recording that prevent a standardized kinematic description of HVLA spinal manipulativetherapy. Despite differences in data between studies, a relationship between preload, peak force, and thrust durationwas evident. Psychomotor learning outcomes were enhanced by the application of thrust data as an augmentedfeedback tool. (J Manipulative Physiol Ther 2010;33:542-553)

Key Indexing Terms: Manipulation, Spinal; Motor Skills; Feedback; Education; Chiropractic

H igh-velocity, low-amplitude (HVLA) spinalmanipulative therapy (SMT) is a key modalityused by chiropractors to treat a multitude of

musculoskeletal and other conditions.1,2 High-velocity,low-amplitude SMT has been shown to have various positivephysiologic effects including biomechanical, reflex neuro-logic, local muscle tone, and pain modulation.1-5 In these andother clinical outcome studies, description of the spinal thrust

hnique Lecturer, Department of Chiropracticrsity NSW 2109, Australia.ndergraduate Studies, Department of Chiroprac-niversity NSW 2109, Australia.rer in Radiological Studies, and Director ofdies, Department of Chiropractic, Macquarie2109, Australia.sts for reprints to: Aron Downie, MChiro, 77ong NSW 2500, Australianie@mq.edu.au).ed October 8, 2009; in revised form May 25une 8, 2010.6.002010 by National University of Health Sciencesjmpt.2010.08.001

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has been rudimentary in terms of the thrust kinematics usedand is often limited to reporting spinal region (eg, cervicalspine) and possibly a vector (eg, rotation manipulation).

Recording high-velocity thrust on human subjects to alevel that allows quantitative data analysis requires one ormore sensing devices, an electronic interface, and often datalogging. This study has critically appraised the variousmethods of measuring HVLA SMT. There is a set ofkinematic variables required to describe the thrust, whichwere commonly used across studies. However, theheterogeneous nature of the studies and the varyingcomplexity of recording devices used have highlightedthe lack of standardization in recording this data.

Just as HVLA SMT clinical outcome studies do notroutinely measure thrust kinematics, studies that reportadverse effects and calculate risks related to HVLA SMT donot describe in any detail the intervention either. Forexample, Assendelft et al6 recommended against “rotarycervical manipulation”; but like other studies of this type,their conclusion relied upon reporting from case reports,surveys, and reviews and not from a quantitative descriptionof the procedure(s). The validity of any recommendation

Fig 1. Study selection process (see Table 1 for MEDLINE searchstrategy).

Table 1. Search strategy example from MEDLINE (OVID)executed January 24, 2010

Terms used # Results

1 spinal manipulation.mp. [mp = title,original title, abstract, name of substance word,subject heading word, unique identifier]

601

2 spinal manipulative therapy.mp. 1803 1 or 2 7284 force.mp. 1049915 4 and 3 636 motor skills.mp. 176797 augmented feedback.mp. 678 6 and 7 209 3 and 7 110 training.mp. 18546011 3 and 10 2812 chiropractic.mp. 388213 11 and 12 1914 mannequin.mp. 45915 manikin.mp. 78116 15 or 14 123417 6 and 16 1018 3 and 16 1

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against applying particular therapy must be questionedwhen based on a less than accurate biomechanicaldescription of the procedure. Triano7 also suggests that inaddition to the lack of objective procedure description, theattributes of those administering the procedure and theirskill level are not well described.

Measurement of the spinal HVLA thrust has also beenused during the training of chiropractic and other manualtherapies to enhance psychomotor skill acquisition andretention. A number of studies exist that describe both thethrust and the change in learning outcomes. We discussthese studies in reference to the mechanism of thrustrecording and the learning implications when that data areapplied as external (augmented) feedback during psycho-motor training. The purpose of this study was tosystematically review studies that quantify the HVLAspinal thrust, to qualitatively compare the apparatus usedand the force-time profiles generated, and to criticallyappraise studies involving the quantification of thrust as anaugmented feedback tool in psychomotor learning.

METHODS

This review has followed the PreferredReporting Items forSystematic Reviews and Meta-Analyses guidelines (Fig 1).8

Data SourcesA search of the literature was conducted up to January

24, 2010, to identify the sources that reported quantificationof the HVLA spinal thrust. The databases included in the

literature search were MEDLINE-OVID (1966-present),MANTIS-OVID (Manual Alternative and Natural TherapyIndex System) (1950-present), and CINAHL-EBSCOhost(Cumulative Index to Nursing and Allied Health Literature)(1981-present). Search strategies were linked to thefollowing MeSH terms and then combined with Booleanfunctions of AND and OR: spinal manipulation, force,motor skills, feedback, training, chiropractic, mannequin,and manikin. The following Non-MeSH terms were alsoused to search the literature, as a significant number ofunique hits were identified in this way: spinal manipulativetherapy, augmented feedback. A full search strategy forMEDLINE-OVID can be found in Table 1.

Eligibility CriteriaTo determine eligibility for a study, the following in-

clusion criteria were applied: performance of the HVLAspinal thrust, recording of single force or force-time ordisplacement-time curves, publication later than 1980, andEnglish language. Studies that tested psychomotor trainingoutcomes, using the HVLA thrust as an augmentedfeedback tool, were also included.

The following exclusion criteria were applied: theoret-ical articles with modeling data only, manipulative studieswith thrust speeds below that required for joint cavitation(eg, graded mobilization, static loads, patient positioningstudies), extremity joint studies, reviews of literature, andconference proceedings. Studies that primarily usedinstrument-based manipulation techniques (eg, ActivatorInstrument) were not included in this review, as the motorpattern needed to deliver thrust is instrument dependent andrequires a skill set different to the manual HVLA thrust.9

544 Journal of Manipulative and Physiological TherapeuticsDownie et alSeptember 2010Quantifying the HVLA Thrust

Furthermore, the force-time profile is determined by thedesign and function of the instrument.10 The selectedstudies were then critically analyzed to compare forcemagnitudes and other relevant parameters required todescribe the HVLA spinal thrust.

Fig 2. Components important to describing the HVLA spinalmanipulative thrust. (1) Preload: the quasi-static load applied tothe soft tissues overlaying the segment to be manipulated. Itspurpose is to compress the soft tissue and to move the joint towardthe limit of its physiologic range. This helps facilitate localizationof the thrust force through the targeted joint and can increasepatient comfort during the procedure. (2) Downward incisuralpoint: the diminution of preload force just before thrust.Commonly termed “run-up” when used in the teaching environ-ment. (3) Thrust speed: speed of delivery of thrust immediatelybefore cavitation. This can also be expressed as time to peak force.(4) Peak force: maximal force exerted into joint. Measured eitherdirectly under contact hand or indirectly from mounted tablesensors (inverse dynamics). (5) Thrust duration: usually measuredas the time from the DIP instance to time of peak force.

RESULTS

Twenty-seven studies met eligibility criteria. Elevenstudies were found that described force-time historiesor single peak forces of HVLA SMT using humansubjects.10-21 Ten studies were found that demonstratedchanges in learning outcomes using measurement of HVLAspinal thrust as augmented feedback.22-31 Two studies werefound that described displacement-time histories HVLASMT using human subjects.32,33 Four studies were foundthat measured HVLA thrust force andmovement parameterson cadavers,21,34 and porcine specimens.35,36 Pooling ofthrust data for further meta analysis was not possiblebecause of the diverse nature of the subjects andpractitioners, methodologies, and instrumentation used torecord information. Studies also often had small samplesizes. Considering that only 27 studies were found (1980–2009), it was decided to include all regardless ofmethodological quality.

DISCUSSION

Studies That Have Quantified the HVLA Spinal ThrustA number of electromechanical devices have been

used to quantify the kinematics of HVLA SMT. Thesestudies are mostly performed on live patients, andthe parameters commonly measured are shown inFigure 2.7,10,13-16,18,19,22,23,25,28,37-39 Table 2 summarizes2 of the more commonly recorded variables, namely, thepreload and peak forces. This is discussed in furtherdetail, with studies grouped by spinal region.

One-dimensional (1-D) or three-dimensional (3-D)recording of the thrust vector can further differentiatestudies. Three-dimensional studies can extrapolate shearforces and torque analysis of the procedure. The sensingdevice can record directly (between practitioner and patient)or indirectly (embedded within treatment table, Fig 3) viainverse dynamics as described by Triano et al.13,29

Embedded load cells measure the total loads from thethrust and practitioner's body simultaneously includingdirection, amplitude, and speed and cannot differentiatebetween the total force used in the procedure and the forceacting on the target joint alone. Data recorded via inversedynamics differ slightly from those of the direct contactsensing method, as found by Kirstukas and Backman,18

often returning a slightly lower peak force for the samethrust on a prone thoracic spine (∼7% reduction).

Contact Interface VariabilityThere are variables to be considered at the interface of

the practitioner's hand and the subject that can influencethrust data. The force acting on a sensorized pad is notevenly distributed. Kirstukas and Backman18 described thedirect sensing method to have an area of greatest forcetransfer often smaller than the total sensing device andcorresponding to the practitioner contact (eg, pisiform).Similarly, Perle and Kawchuk24 studied the effects of handshape (flat hand or arched hand) during a prone thrust. Peakforces via a pressure plate and location of force viaradiographic analysis revealed a relationship between themagnitude, location, distribution of pressure, and the handshape chosen. They concluded that clinical efficacy/safetymight be influenced by the choice of hand shape, astherapists in the field will empirically attest to. Effectiveforce transmission over the target joint was examined byHerzog et al14 who determined that the average peak forcerecorded by a prone thoracic HVLA thrust over the wholecontact area was 238.3 N, but the average peak force overthe transverse process target area of 25 mm2 (resolution ofthe sensor mat used) was only 5 N. They argued that muchof the contact force is not specific to the treatment but istransmitted to adjacent soft tissues. Kirstukas andBackman18 measured the surface area covered at the peakof thrust and averaged an intense target surface area of 870mm2 (±610). The sensing “puck” used by van Zoest et al12

and van Zoest and Gosselin19 had a contact base of 26 cm2

Table 2. Resultant preload and peak forces noting sensing device and intervention

Year AuthorPatient position, sensing device,and dimensions recorded Remarks

Mean preloadforce (±SE) (N)

Mean peakforce (±SE) (N)

Cervicalspine

1992 Kawchuck et al16 Side posture toggle recoilmethod (1-D)

101.7 (±14.7)

1993 Kawchuk andHerzog10

Various patient positionsPressure pad attached to subjects'neck (1-D)

Lateral break 39.5 (±4.9) 102.2 (±46.8)Gonstead 24.7 (±6.5) 109.8 (±5.6)Activator 21.9 (±5.2) 40.9 (±2.8)Toggle 1.9 (±1.9) 117.6 (±6.4)Rotation 29.1 (±4.3) 40.5 (±4.5)

1993 Herzog et al15 Side posture toggle recoilmethod (1-D)

117.7 (±15.6)

2003 van Zoest andGosselin19

Supine @ C5Handheld sensor “puck” againstsubject's spine (3-D)

32 (±10) 110 (±12)

Thoracicspine

1993 Conway et al20 Prone unilateral pisiform overTP @ T4Pressure pad and skin-mountedaccelerometer to register force attime of cavitation (1-D)

Preload/peak forceForce @ cavitation

145 (±54) 400 (±118)364 (±106)

1994 Gal et al21 Prone unilateral pisiform over TPPressure pad over prone cadaver @T11 with accelerometers, and bonepins monitored by camera (1-D)

68.9 (±17.4) 518.5 (±70)

1999 Kirstukas andBackman18

Prone reinforced unilateral pisiformUnder hand: pressure pad (1-D)In support: 2 table-mountedload cells (3-D)

310 (±62) 1044 (±186)

2001 Herzog et al14 Prone U/L pisiform T3-T10Pressure pad (1-D)

Total areaTarget Area

23.8 (±24.5)7.8 (±7.3)

238.2 (±45.9)34.8 (±8.9)

2003 van Zoestet al12,19

Prone @ T4 and T8Handheld sensor “puck” againstsubject's spine (3-D)

T4T8

227 (±30)226 (±31)

561 (±61)518 (±48)

2004 Forand et al11 Prone @ T4Pressure pad male vs female (1-D)

MaleFemale

137 (±58)138 (±63)

462 (±194)482 (±130)

2005 Descarreauxet al17

Prone U/L hypothenar instrumentedmanikin, and under foot forceplate (1-D)

2nd y student5-y clinical experience

31 (±20)44 (±63)

570 (±27)544 (±29)

2006 Descarreauxet al23

Prone U/L hypothenar instrumentedmanikin, and under foot forceplate (1-D)

Student pretrainStudent posttrain

59.2 (±16.2)176.7 (±17.3)

630.9 (±35)538.4 (±16.9)

Lumbopelvicspine

1997 Triano andShultz13

Side postureTable-mounted load cells (3-D)

L5 mamillary pushL5 long leverSacroiliac push

495 (±142.5)384.7 (±114.1)515.5 (±123.8)

2003 van Zoest andGosselin19

Sacroiliac: side postureHandheld sensor “puck” againstcontact point (3-D)

83 (±15) 241 (±57)

2004 Triano et al26 Side posture mamillary push @ L4Table-mounted load cells (3-D)

Inexperienced studentExperienced student

210.2 (±106.5)321.4 (±112.6)

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(2600 mm2). This suggests that the contact interfaceapparatus and practitioner contact area must be taken intoaccount if the data across various studies are to becompared. Unfortunately, the majority of studies revieweddid not consider the size of contact area at all.

As can be seen in Table 2, the majority of devices thathave recorded thrust kinematics use the prone thoracicspine. Recording in this region can be relatively simple, asthe thrust vector is usually perpendicular to the patient/table/sensing device, making it relatively simple to create a3-D analysis, either directly or via inverse dynamics. Sideposture cervical thrusts have also been measured through a

table toggle device in this manner. Measurement of lumbaror sacroiliac HVLA thrust is more complex because itnecessitates positioning the patient in side posture, andposterior-to-anterior thrust vector is no longer perpendic-ular to the sensing plate embedded in the table. Thisrequires a 3-D analysis to describe the thrust. Largevariations in force between spinal region and betweenstudies on the same region have been observed. Variablesinfluencing thrust data are discussed in detail below andsummarized in Table 3.

In a review of the literature on lumbar spine mobiliza-tion, Snodgrass et al40 found similar large variability

Fig 3. Representation of sensor placement across studies.

Table 3. Variables influencing thrust data

Category Variables

Patient/subjectstatus

Age, pain state, degenerative state, cadaver

Spinal region Facet morphology, tissue compliancePractitioner

experiencePractitioner clinical training, familiaritywith the technique and sensing device

Manualtechniquechoice

Patient positioning, spinous or transversecontact, hand profile, pretension style(assisted or resisted model of adjusting)

Sensor type 1-D/3-D, direct sensing/inverse dynamics;size, thickness, and stiffness of sensingmaterial (metal or flexible polymer);data accuracy (resolution, linearity, drift, hysteresis)

Apparatus setup How closely it mimics a typical clinical setting

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between studies and concluded that such variability indefinitions is problematic for defining and exploring theliterature. They concluded that variation in technique,measurement/reporting procedures, or therapist/patientvariation was responsible for the variability observed.This review corroborates the findings of Snodgrass et al.

Cervical SpineAs early as 1993, Kawchuk and Herzog10 measured the

force profiles of 5 commonly used techniques formanipulation of the cervical spine by attaching a 1-Dsensor pad to the subjects' skin. They found that the thrustprofile was dependent upon the technique used, the speed ofapplied force before substantial preload was applied, andhow soon a second thrust was attempted. The secondattempt, if performed a few seconds after the first, wouldoften result in a successful cavitation. van Zoest et al12 and

van Zoest and Gosselin19 used a handheld recording deviceto measure the 3-D contact force via an instrument placedbetween the practitioner and the skin of the supine patient.This allowed force-time histories to be generated in 3dimensions during supine midcervical thrust. They foundthat the sum of the individual force components generatedwas significantly greater than the perpendicular (1-D) forcecomponent. They commented on the lack of 3-D modelingof forces generated during thrust in other studies andsuggested that 3-D modeling provides a more completedescription of the thrust.

A novel noncontact measurement of tracking HVLAthrust was performed by Triano and Schultz33 who used anoptoelectronic system with targets placed on the chest andhead of a supine patient, monitored by cameras around theroom. Movements of head and thorax during prepositioning(preload) and thrust applied during SMT of C2 in “direct”and “rotary break” maneuvers were recorded. They foundthat the upper cervical spine is placed in near maximalrotation and lateral bending during both maneuvers. Theyconcluded that SMT can be successfully modified to controlamplitude and displacement. Although this study did notrecord forces exerted, a displacement-time curve withsimilar key features of the force-time curve was generated.Klein et al32 also used noncontact tracking of headmovement during cervical spine HVLA manipulativetherapy. They used 3-D goniometers to track headmovement during seated manipulation and demonstratedan ability to record flexion, lateral bending, and rotationvectors independently.

Ngan et al36 studied the angular displacement of anadjacent vertebra during a simulated rotational manipula-tion of a porcine cervical spine. They found that adjacent

547Downie et alJournal of Manipulative and Physiological TherapeuticsQuantifying the HVLA ThrustVolume 33, Number 7

vertebral movement was related to the input angulardisplacement and the thrust velocity. They recommendedmoderating both the angular displacement and the thrustvelocity so as to minimize the viscoelastic effect onbiological tissue, which produces an increase in tissuestiffness with velocity increase. This can have the clinicallyundesirable effect of transmitting the target force toadjacent, not target, joints.

Cervical spine studies that measure force-time para-meters of the thrust where the patient is supine are few.When we consider the significant skill required to masterthe supine cervical thrust41 and the risk of undesirablesequelae, the need for further study in this area is evident.

Thoracic SpineHerzog et al15 used a flexible pressure mat placed onto a

subject to record the thrust delivered (single axis) in a force-time history. Regions tested included prone thoracic,lumbopelvic, and lateral cervical spine on a drop piece.They found a strong relationship between preload force andpeak force used in thoracic manipulation (FMax:FPreload =2.5:1) and weaker but similar relationship for sacroiliacjoint manipulation. The preload used in a clinical procedurefor lateral cervical thrust was considerably less than initiallythought. This was also found by Kawchuk et al,16 who alsoobserved that a direct sampling method (detection at thepractitioner-patient interface) returned a shorter thrustduration when compared with studies that placed the sensoron the table beneath (inverse dynamics).28,29 It washypothesized that the longer times observed were artifactsof the damped oscillatory system (patient and treatmenttable). Direct recording at the patient-practitioner interfacemay therefore be superior in measuring thrust duration andmeasuring the joint specific (target) force, whereas inversedynamics records 3-D data from the total procedure.14

Cohen et al38 were one of the first to pay significantattention to the downward incisural point (DIP, Fig 2) anduse it as a predictor of experience. An increase in themagnitude and/or number of DIPs represent a “run-up” orbacking off just before thrust execution. This is undesirablefor many reasons, including the slackening of tissue directlyunder the contact hand and a possible reduction in targetspecificity. The same study compared novice vs experiencedpractitioners performing a thoracic bilateral transversethenar HVLA thrust that was unfamiliar to both groups,and found that although the mean force values were higherin the experienced group, no systematic differences inmeasured values between the 2 groups existed. Theysuggested that regular use of a procedure was necessary indeveloping the skill.

Descarreaux et al17 placed a load cell in a prone thoracicmanikin embedded with an electromagnetic switch tosimulate cavitation. He described time to peak force, timeto peak force variability, peak force variability, rate of force

production, and unloading time measured from the forceplate and averaged for experienced and inexperiencedpractitioners. Hand-body delay was measured by compar-ing the time lag between the onset of unloading the floor-mounted practitioner force plate (Fig 3) and the onset ofpeak force production. This value was used as a measure ofcoordination during the thrust. Unlike Cohen et al,38

Descarreaux et al17 found that the level of experience didinfluence the peak force, preload force, and peak forcevariability. A later study with similar apparatus measuredthe effect of augmented feedback on training and isincluded in Table 4.23

Kirstukas and Backman18 generated force-time historiesduring thoracic SMT using both direct measurement via asensor mat placed on the patient and indirect measurementusing load cells placed under the treatment table. The sensormat they used generated both dynamic force and spatialpressure distribution, such that a plot of distributed contactpressure was produced. They agreed with Herzog et al15

that there is a linear relationship between the preload andpeak forces during SMT. They also found that the (table-floor) load sensors returned a lower peak force reading but,unlike Kawchuck et al,16 did not measure the thrustduration differences between the 2 sensing devices.

The flexible pressure pad of Herzog et al was used byForland et al11 to record force differences during pronethoracic HVLA manipulation between male and femalepractitioners. The only significant variations were those ofpreload force applied to lower thoracic spine, which weregreater for the male participants. They concluded thatfemale chiropractors produce similar thrust mechanics astheir male colleagues when considering preload and peakforce production. This is an important finding because,clinically and pedagogically, there seems to be littledifference between male and female practitioners in thedelivery of the therapeutic HVLA thrust.

Conway et al20 used a pressure pad between the patientand practitioner and recorded forces at the instant ofcavitation by synchronizing a skin-mounted accelerometerover the spinous process of adjacent vertebral bodies.They found that cavitation occurred just before peak forcein 8 of 10 thrusts and just afterward in 2. The peak forcewas greater in a successful cavitation at T4 whencompared with an unsuccessful procedure. Given thedata gathered, the authors could not isolate all of thefactors necessary for cavitation, but suggested that it is“either a function of a complex interaction of manymechanical variables, or is caused by different factors fordifferent patient/treatment combinations.”

Lumbopelvic RegionTriano and Schultz13 measured loads transmitted

through the lumbosacral spine onto a force plate usingapparatus used in later studies also.22 ,27-29 They

Table 4. Summary of studies using augmented feedback for teaching HVLA SMT

Author Body region Mechanical device Feedback recording Methods summary Key indings Learning implications

Young et al31 1998 C° supine TMC manikin Experienced observer(tutor for both groups)

20 chiro 4th ystudents in 2 groups

No gnificant differencesbetw en 2 groups duringOSC examination

Training C° HVLA witha TMC manikin insteadof a live “patient” is aseffective as standardtraining for 4th ychiropractic studentsunder regulartuition conditions

Standard teachingManikin only

Scaringe30 2002 T° prone Piezoelectric film infoam rubber

Single voltage reading(single axis)

71 chiro 2nd ystudents thrustingover time using “heavy”or “light” HVLAthrust in 2 groups

↑Fo e accuracygrea st withqua itative f/btow d end of trial

Students' learning isenhanced using kineticdevices with bothquantitative andqualitative f/b. Studentsneed sufficient learningtime to benefit fromdetailed (quantitative)information

U/L hypothenartransverse

Qualitative f/bQuantitative f/b

Triano et al29 2002(Rogers andTriano,27 forinstrumentvalidation)

L5 mamillary push Modified Leandertable withAMTI force plate,artificial 2°arm support &student as patientDynajust instrument

Load-time historyPt VAS onstudents' performance(3 axis + 3 moment)

39 chiro studentsEstablish baselinecurve using modifiedtable. 2 groupsStandard trainingStandard training +Dynajust

↑FP load, ↑FMax, ↑speedin D najust group↑VA (pt reporting) oncom rt, speed, force,prec ion, confidence inf/b oup

Using the Dynajustinstrument improvesall parameters ofHVLA skill acquisitionwhen compared withstandard training.A modified Leandertreatment table can beused to effectivelytrack student progressin skill acquisition

Triano et al28 2003 C2 prone indexpush & T7 pronepisiform-transversethrust

↑Speed of C° & T°in Dynajust groupAbility to modifythrust vectorappropriately inDynajust group

Using the Dynajustinstrument improvesall parameters ofHVLA skill acquisitionwhen compared withstandard training.A modified Leandertreatment table can beused to effectivelytrack student progressin skill acquisition

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Triano et al26 L4 mamillary push Modified Leandertable withAMTI force plate,artificial 2°arm support & studentas patient

Load-time history 38 inexperienced students ↑FMax, ↑speed instudents withexperience

Students with therelevant prerequisitesin HVLA trainingperform to a higherlevel at a single taskthan students without

39 experienced students

Inexperienced:FMax = 210.2 (±106.5)Experienced:FMax = 321.4 N (±112.6)

Enebo andSherwood25

2003

T° prone Mechanically sprungdevice simulating aP-A thrust intoa cadaver

Load-time history(single axis)

33 chiro students years 1-4 Greatest consistency(↓ ΔFMax)when combiningrandom variablepractice + visualf/b + experience

Students modulate thrustforces with mostaccuracy when targetforces vary randomlyand use visualquantitative f/b. Studentsbenefit most fromscheduling ↑blockpractice during the early(acquisition) phase oftraining and fromscheduling ↑variablepractice in laterstages (retention)

Establish FPreload = 20%FMax

↑Acquisition withblock practice

Serial trials consisting ofvarious levels of FMax inblocked and random order.2 groups

↑Retention withvariable practice

KP (verbal) f/bKP (visual) f/b

Triano et al22 2006 L4 mamillary push Modified Leandertable withAMTI force plate,artificial 2°arm support &student as patient

Load-time history 40 inexperiencedchiro students

↑Speed from f/b group Acquisition andretention of specifickinematic skill in anovice operator can beenhanced by visual f/bKR and is consistentwith the pt's VASreporting of the event.The acquired skill isretained for a shortperiod even aftera distractive task

Pt VAS on students'performance Establish baseline

curve usingmodified table. 2 groups

↑VAS (pt reporting) oncomfort, speed, force,precision, confidence inf/b group

(3 axis + 3 moment)

No f/b trainingVisual f/b tomatch experiencedthrust dynamics, then“distraction” for 10 min

Descarreauxet al23 2006

T° prone pisiformthrust

Modified CPR manikin(load cell, spring,electromechanicalswitch set to 475 N)

Force-time history ofboth manikin andoperator

31 4th y students Both groupsdemonstrated reductionin ΔFMax, FMax

(631 to 538 N) and DIPs(10.5 to 7 trials), with thef/b group showingmost reduction.

The augmented f/bgroup returned betterperformance in allparameters consideredimportant in learningHVLA thrust, namely,increasing preload,reducing DIP, reducingmaximum force tocavitation, and reducingpeak force variability

Force plate underthe operator

Establish baselinecurve using manikin.2 groupsStandard tuition

↑FPreload demonstratedin the f/b group only(66 to 177 N)

Visual f/b

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investigated 3 types of HVLA manipulation procedures(mamillary push, hypothenar-ischial, and long lever) andrecorded the force-time histories. They found that themaximum forces were similar and dependent only upon thepatient positioning and body mass of the practitioner, witheach thrust type displaying a unique vector profile. Anadditional parameter of this study was to record thecontraction of key spinal muscle groups in the patientduring the thrust procedure. Myoelectric activity wasfound to be negligible, and the authors concluded that thepatient was not adding to the loads recorded via his or herown muscular contraction. They questioned whether thisfinding would be true for a study using symptomaticpatients as opposed to students familiar with the relaxationexpected for a successful execution of thrust. Approxi-mately 10 years later, Owens et al42 found no relationbetween the severity or chronicity of low back painpatients and their spinal stiffness. However, they did notrecord myoelectric activity. Using the apparatus of Trianoand Schultz,13 Tsung et al43 measured the loads acting onthe lumbar spine during mobilization into rotation. Theauthors found that rotational mobilization of the lumbarspine increased movement in all 3 motion planes. Theyinferred that clinical application of such mobilization couldbe used to restore motion in other planes.

As with the cervical spine, van Zoest and Gosselin19 usedtheir handheld puck to measure contact forces in the pronethoracic and side posture sacroiliac HVLA manipulativeprocedures. The authors also found, similar to Cohen et al,38

that DIP recorded was a key feature of the thrust profile.Descarreaux et al23 also used the DIP as an outcomemeasure in determining the effect of augmented feedback inmanipulation training. Adding weight to the importance ofminimizing DIP during thrust execution, the frictionalproperties of the thoracic skin-fascia interface and itsimplications to SMT were examined by Bereznick et al.44

They found that, to maintain the original contact positionduring thrust, it was necessary to maintain skin slack duringthe thrust, which is consistent with a low-magnitude DIP.

Gal et al21,34 used unembalmed human cadavers todetermine the relative movements and change in position ofthe lower thoracic spinal segments during HVLA SMT.They also measured the preload and peak forces applied tothe transverse process of T11. They tracked movement byvisual recording of bone pins and force by direct contactpressure pad. They found that the relative sagittal rotationsbetween vertebrae were significant and that motion wasinfluenced largely by the facet morphology. They expectedto see similar trends in living patients.

Role of HVLA Thrust Recording in Psychomotor AcquisitionTraining of chiropractic students in thrust techniques

requires considerable time and skill from both the studentand teacher. The rate of skill development that a student will

attain in a motor control task is dependent upon both thequality and quantity of internal and external feedback forthat task.45 Traditionally, feedback on student performanceis given via an experienced tutor/clinician, who willcomment on either a part or the whole of the thrustperformance.46 Parameters observed during student assess-ment regularly include thrust vector, preload force,amplitude, velocity, and general coordination/positioningof the student. This assessment is qualitative in nature andrelies on an assessor's opinion of the procedure. Errors infeedback consistency relating to tutor access, tutorexperience, differing opinions, and observational powerscan occur, limiting the progression of the student. Incontrast, quantitative assessment of the thrust has beenshown to be superior to qualitative observation for many ofthe criteria by which progression in psychomotor training ismeasured. A summary of these studies with their keyfindings is shown in Table 4, followed by an overview ofpsychomotor learning relevant to these studies.

The HVLA spinal thrust requires bimanual coordinationand often that of the practitioner's whole body.41,47

Because motor learning difficulty increases relative to thecomplexity of the task,39,48 how we learn can be used as abasis to teaching this skill more effectively.22 As studentstrain and later enter the profession, it is important that theyprogress through a continuum of motor learning from“basic safety” through “functional adequacy” and to “skillmastery.”49 Therefore, the instructor needs to know whatstyle of feedback to give at different stages of learning.23,38

There are 2 main types of augmented feedback useful to themanual therapy instructor. The first is knowledge ofperformance (KP), which references the pattern ofmovement in achieving the goal. The second is knowledgeof results, which refers to the outcome achieved.Augmented feedback can be either qualitative (eg, tutortraining via observation/instruction) or quantitative,22 asare the kinematics of the HVLA thrust discussed in thisreview. A detailed analysis of skill acquisition and of thevarious ways to apply augmented feedback has beenexplored by Schmidt.50

The variables measured in augmented feedback studiesare similar to those used to quantify the HVLA thrust.Without exception, the augmented feedback groups per-formed to a higher standard than control groups; or theenhanced training was able to replace standard trainingwithout detriment to complex skill acquisition. Positiveoutcome measures (those that were seen to enhancelearning) are described in Table 5.

The complexity of the apparatus used ranges from asimple cervical spine rubberized manikin31 to elaboratemodification of treatment tables such as adding secondarystabilizing arms and force plates.22,28,29 In addition tomodified thrust apparatus, load cells have been placed underpractitioner's feet.23 Forms of augmented feedback rangefrom a simple single-axis peak voltage reading30 to

Practical Applications• No standard exists for HVLA thrust recording, andthe variation in sensing device and methodologiesmakes quantitative analysis between studies

Table 5. Outcome measures used to determine skill acquisition

Quantitative outcome measure Author

Increase in peak forceconsistency (↓ΔFMax)

Scaringe,30 Enebo and Sherwood,25

Descarreaux et al23

Increase in preload (↑FPreload) Triano et al,28 Triano et al,22

Descarreaux et al23

Increased peak force (↑FMax) Triano et al28

Decreased peak force to matchtarget (↓FMax)

Descarreaux et al23

Increased thrust speed (↑dF/dt) Triano et al,28 Triano et al,22

Descarreaux et al23

Reduction in DIP Descarreaux et al23

Manikin training vs standard(live model) training

Young et al31

Positive patient (VAS) reporting Triano et al,28 Triano et al22

551Downie et alJournal of Manipulative and Physiological TherapeuticsQuantifying the HVLA ThrustVolume 33, Number 7

elaborate real-time screen readouts of force-time histories.23

Augmented training apparatus in some studies was thefeedback device itself,23,25,30,31 fellow student body, or anauxiliary instrument such as the Dynajust device.28,29

difficult.• Trends exist within the data to demonstraterelationships between components of the thrust.

• It is recommended that standardized kinematicanalysis and recording methods be established toenable a complete description of the interventionwhen assessing the clinical efficacy of HVLASMT.

LimitationsAs the bulk of the studies used different sensing

methods and differing methodologies, a meta-analysis ofthe studies was not possible. There are a large number ofvariables that influence the thrust profile and magnitude, ashave been shown in Table 3. Many studies did not accountfor these variables. For example, not all studies describecompletely the sensing apparatus with regard to thepractitioner's contact surface area, whether the sensingdevice itself influenced the motor pattern of the practition-er, or whether the forces across the mat were differentiallyrecorded. The search strategy would have missed any non-English publications.

CONCLUSION

There exist quantifiable parameters that describe theHVLA spinal manipulative thrust. Thrust magnitudes havebeen extracted, and the large variance in magnitude foundbetween studies has been discussed. Despite this variance,trends exist within the data that demonstrate relationshipbetween the preload, DIP, peak force, and thrust durationof a single thrust. Positive learning outcomes were alsofound when using the HVLA thrust as an augmentedfeedback tool.

This review highlights that, for direct contact recording,force distribution across the device (mat) can vary greatlyand depends upon the practitioner hand dynamics andstiffness of the device. Furthermore, the total force recordedboth directly and via inverse dynamics may grosslyoverestimate the force delivered to the spinal target (eg,transverse process). It is recommended that future studiesdescribe both the total force delivered and the effectiveforce over the target.

If the claimed clinical efficacy or health risk related toHVLA SMT could be measured in the context ofkinematics that delivered the thrust, any relationshipbetween the intervention and outcome could be establishedwith greater confidence. Unfortunately, existing clinicaloutcome studies have described the thrust intervention onlyin the most rudimentary of qualitative terms. Therefore, it isrecommended that standardized kinematic analysis andrecording methods be established to enable a completedescription of the intervention when assessing the clinicalefficacy of HVLA SMT.

FUNDING SOURCES AND POTENTIAL CONFLICTS OF INTERESTNo funding sources or conflicts of interest were reported

for this study.

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